The present invention relates to a process for preparing an electrically conductive polymer, more particularly a polyaniline, a polypyrrole, or a polythiophene. Polyanilines, polypyrroles, and polythiophenes are a class of stable, intrinsically conductive, conjugated polymers, the electrical properties of which can be controlled by the degree of doping. As such, these electrically conductive polymers are useful in a variety of electrical, electrochemical, electroactive, and optical applications. Teachings of these electrically conductive polymers and their uses can be found in a number of publications, including U.S. Pat. Nos. 3,963,498; 4,025,463; 4,983,322; and 5,415,893.
Polyanilines, polypyrroles, and polythiophenes can readily be prepared from anilines, pyrroles, and thiophenes using chemical or electrochemical oxidative polymerization methods well known in the art. For example, chemical oxidation of aniline is carried out in aqueous acid solutions and in the presence of an oxidant, most notably ammonium persulfate. (See for example, U.S. Pat. Nos. 4,604,427; 5,324,453; and 5,371,182; and Cao et al. in Polymer, Vol. 30, pp. 2305-2311 (1989)). Although persulfates are among the most effective and widely used oxidants, they are expensive. Therefore, it would be desirable to find an alternative oxidant that promotes the formation of highly electrically conductive polymers at high yields.
Ferric chloride is a common oxidant used particularly for pyrroles and thiophenes. Inasmuch as ferric chloride use leads to significant problems in waste disposal, it would further be advantageous to discover an oxidant that, at the very least, reduces the amount of ferric chloride required to produce the polymer in acceptable yields.